Nuclear Physics The Atom

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1 Nuclear Energy 1

2 Outline Outline Science of Nuclear Energy History Current Importance Dangers of Nuclear Power Future Potential Resources Boyle, Everett, Ramage Energy Systems and Sustainability International Atomic Energy Agency OECD Nuclear Energy Association World Nuclear Association (Nuclear Professions) Nuclear Information Resource Centre (Anti-Nuclear) World Information Service on Energy 2

3 Nuclear Physics The Atom Bohr Model of Atom A concentrated Nucleus (containing Protons and Neutrons) with a cloud of orbiting electrons. The number of protons in the nucleus is ca;;ed the atomic number and determines the element (e.g. Oxygen has 8 protons, Uranium has 92). The number of neutrons in the nucleus can vary resulting in different isotopes of the same element. The isotopes will behave identically in chemical reactions but have differing atomic mass. Only certain isotopes are stable. Protons and Neutrons have similar mass (approximately 1 atomic mass unit) and isotopes are usually identified by their atomic mass which is the total number of protons and neutrons in the nucleus. E.g Carbon-12 has 6 protons and 6 neutrons. Carbon-14 has 6 protons and 8 neutrons. Bohr Model of Atom UTC Physics Dept. website: 3

4 Fission and Fusion Chemical reactions involve the interaction of electrons and the combination of atoms into molecules. The energy released or consumed is due to electrical forces. Nuclear energy involves the splitting (fission) or combining (fusion) of nuclei of some elements to make entirely different elements. The nuclear forces involved are many times stronger than electrical forces and the energies released are much greater. The periodic table lists all elements in order of atomic number. It turns out that nuclei near the centre of the table (Iron) are in the most stable lowest energy state. Any nuclear reaction which results in elements from the opposite ends of the table changing into elements closer to the centre will result in the excess energy being released. In Fusion light nuclei such as Hydrogen fuse together to form a heavier nucleus. In Fission a heavy nucleus such as Uranium breaks apart to form lighter nuclei. 4

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6 E= mc 2 Einstein s formulation of the equivalence of mass and energy (E=mc 2 ) provides a method for calculating the energies released if we know the mass of the starting nuclei and the mass of the products. Contrary to what you may have heard matter is not destroyed during conventional nuclear reactions. The total number of protons and neutrons does not change before and after. The energies released are so great that there is a measurable difference in mass before and after. In theory E=mc 2 could be used to measure the energies released in a chemical reaction but the percentage change in mass involved is too small too measure. Boyle Everett and Ramage calculate the energy released from the complete fission of 1kg of Uranium-235 and show that it is equivalent to the combustion of about 3000 tonnes of coal. 6

7 Danger Hazardous Radiation In addition to the new elements formed nuclear reactions typically emit high energy electromagnetic radiation (gamma rays) and fast moving particles (alpha particles, neutrons, beta particles). These ionisong radiations are extremely hazardous to living organisms. In a nuclear reactor steps are taken to force nuclear reactions to occur but many heavier elements are inherently unstable and the nucleus will decay spontaneously emitting dangerous radiation, given time. Such materials are said to be radioactive and they can remain hazardous to life for many thousands of years. The term half-life is used for the period it takes for radiation levels from a sample to decay to 50% of their initial value. For example the plutonium isotope 239 Pu for has a half life of 24,000 years. A particular hazard of nuclear fission is that the fuels and the products of fission are highly radioactive presenting significant difficulties in handling, storage and disposal. 7

8 Some important nuclear reactions Fusion Deuterium/Tritium Fusion 2 H+ 3 H 5 He 4 He+neutron+energy Needs very high temperature to initiate Fission Uranium-235 chain reaction 235 U+ neutron Fission Products+neutrons+energy Plutonium Creation 238 U+ neutron 239 U 239 Np+β 239 Pu+β Note that in More standard nuclear notation : U+ 1 0 n β U 23minutes β Np 2.3days Pu 8

9 Fast Neutrons Slow Neutrons In order for a sustained fission reaction to occur in 235 U then at least one of the neutrons emitted from a fission must collide with another 235 U nucleus and cause another fission chain reaction. The neutrons emitted with high energy travel very fast and in natural uranium most of them will pass right through the material and a chain reaction doesn t occur. Solutions to the problem of fast neutrons Increase the concentration of 235 U Increase the amount of fissile material (fast neutrons more likely to be caught in a bigger lump of uranium). critical mass used in bombs. Slow down the neutrons with a moderating material slow neutrons (called thermal neutrons) spend longer in the material and are more likely to collide with a 235 U nucleus and cause a chain reaction. Commonly used in nuclear power stations. 9

10 History of Nuclear Energy Early 1900 s: Discovery of nature of the Atom, Einstein s discovery of mass-energy equivalence Discovery of Fission of Uranium 1942 first nuclear reactor (Chicago- Fermi) Manhattan project development of Fission Bomb 1950 s First generation of nuclear Fission reactors 1960 s Commercial Nuclear (Fission) power generation in USA / Canada / UK / USSR/ France 2 nd Generation reactors. Late 1970 s Nuclear Brown-Out. Nuclear arms limitation talks, concerns over safety and environmental impact stagnation. New plant orders cancelled Third generation (Fission) reactor technology, dwindling fossil fuel supplies, concern over greenhouse gas emissions have revived the prospects for nuclear power. Possible Nuclear Renaissance. Sources: US Department of Energy Booklet DOE/NE-0088 The History of Nuclear Energy Australian Uranium Association Outline History of Nuclear Energy available online at accessed 19/11/

11 The Dark Side of Nuclear Power Nuclear Weapons August 1945 Japanese Cities of Hiroshima and Nagasaki destroyed by fission bombs 1950s & 1960s The Cold War: A nuclear arms race develops between USA and Soviet Union. Development of increasingly powerful fission and fusion based weapons technology. Policy of Mutually Assured Destruction Nuclear Arms proliferation: USA (1945), USSR (1949), UK (1952), France (1960), China (1964), India (1974) The Cold War ended in early 1990 s but nuclear arms proliferation continues: Pakistan (1998), Israel (?), Saouth Africa (?), North Korea (1996). But Nuclear power generation has nothing to do with bombs or does it? Nuclear Reactors Create the Material and Technological Expertise to Make Nuclear Weapons Greenpeace USA Significant Nuclear Accidents: 1957 Windscale (Site now known as Sellafield), UK 1979 Three Mile Island, USA 1986 Chernobyl, Ukraine Worlds worst disaster. Over 300,000 people evacuated Tokaimura (Unanticipated criticality in Uranium reprocessing plant, 2 deaths 119 people received significant doses of radiation), Japan Source: Atomic Archivehttp:// 11

12 Uranium fuel fabrication Uranium is farily widespread in many types of rock almost always occurring as the oxide U 3 O 8 High grade ore will have a few percent of U 3 O 8. Initial processing extracts pure U 3 O 8 (yellow cake). Natural Uranium is mainly composed of 238 U (99.27%) but 235 U (0.72%) is the important isotope for fission. Enrichment usually takes place at this stage to increase the percentage of 235 U. Commercial reactors typically use fuel with 3-5% 235 U but certain reactor types need highly enriched fuel with more than 20% 235 U. Highly enriched Uranium is also suitable for use in nuclear weapons. After enrichment the U 3 O 8 is further processed to produce either metallic Uranium or more commonly pellets of the oxide UO 2. 12

13 Fission Reactors All reactors generate heat which is used to create steam or hot gas. This in turn may be used to drive a turbine which generates electricity. Key Terminology: Thermal Reactor: Uses Slow Neutrons (called Thermal Neutrons) to maintain reaction Fuel: Most commonly enriched Uranium in UO 2 form Moderator: Slows down emitted neutrons in order to maintain the reaction. Light Water/ Heavy Water/ Graphite can be used. Coolant: Fluid used to take heat away from the reactor. May double up as a moderator. Control Rods: Neutron absorbing material (Boron/Cadmium) used to remove neutrons and control the rate of reaction Shielding: Blocks the dangerous radiation coming from the core (thick layer of concrete) Containment: ensures that none of the radioactive material can escape. 13

14 Common Types of Fission Reactor Reactor Fuel Moderator Coolant Pressurised Water Reactor Enriched Uranium Light Water Light Water Most Common Reactor Type Today Boiling Water Reactor Enriched Uranium Light Water Light Water/Steam Second most common. Uses coolant directly to drive turbine Magnox Natural Uranium graphite CO 2 Older UK Design Advanced Gas Cooled Reactor Enriched Uranium graphite CO 2 Unsuccessful British rival to PWR Canadian Deuterium- Uranium Natural Uranium Heavy Water Heavy Water Canadian design that can use natural uranium VVER Enriched Uranium Light water Light water Russian equivalent of PWR RBMK Enriched URanium graphite Light water/steam Russian Design Liquid Metal Fast Breeder Reactor Highly Enriched Uranium none Liquid sodium Breeder reactors convert depleted 238 U into Plutonium 14

15 Pressurised Water Reactor Source: Hyperphysics 15

16 Boiling Water Reactor Source: Hyperphysics 16

17 Liquid Metal Fast Breeder Reactor Source: Hyperphysics 17

18 Uranium Reserves and Production Uranium Production was running at 41ktonnes per annum in 2005 and proven reserves were 3.3Mtonnes recoverable at up to $130/kg according to the World Energy Councils 2007 survey of World Energy reserves. That implies we have enough uranium left for another 79 years at current rates of consumption. However Uranium is widely distributed througout the Earth at low levels of concentration so the total amount of uranium is probably much greater. The World Energy Council predict that yet to be discovered reserves may bring the recoverable figure up to 7.5 Mtonnes. The European Nuclear society suggests that the total amount of Uranium may be as high as Million tonnes. The use of reprocessing (which extracts additional fissionable material from spent fuel) and fast breeder reactors (which convert U-238 to fissionable plutonium) could multiply the life of uranium reserves many times over. 18

19 2007 Survey of Energy Resources World Energy Council 19

20 Importance of Nuclear Power Source: World Coal Institute accessed 12 Nov

21 Nuclear Share of Electricity Generation Source: IAEA 2007 Energy Electricity and Nuclear Power Estimates for the period up to 2030 available online from 21

22 Economics of Nuclear Power Even though uranium processing is expensive the incredible energy density means that fully fabricated fuel only costs about a third of the fuel cost for a coal fired plant (Boyle Everett Ramage). Nuclear generation can seem very competitive if only the operating costs are considered. However the capital cost of the plant is much higher than for conventional generation (factor of three BER). In fact fuel only accounts for some 20% of the overall cost of nuclear generation (BER). Fossil fuel based generation gives rise to the externality of greenhouse gas emissions. In some countries (Europe) this is being factored into the price through emissions trading. Nuclear Power generation has significant externalities in both waste disposal and also decommissioning costs and if these were factored in to the price of nuclear generation it could alter the economics significantly. 22

23 Source: Nuclear Energy Institute 23

24 Source: Sokolov & McDonald Nuclear Power Global Status and Trends Publication of International Atomic Energy Agency available online from iaea.org Q. Do these figures include externalities related to pollution, waste reprocessing or decommissioning? 24

25 Nuclear Waste Low Level waste (from outside the shielded reactor core) may be dealt with by short term storage for periods of 50 years or so by which time the residual radioactivity will have decayed to safe levels. High level waste materials from within the reactor core will remain hazardous for thousands of years and a long term solution is required. Storage undersea or underground has been considered but stable geological conditions are required. 25

26 Reprocessing Typical Constituents of Spent Fuel (BER) U-235 (0.7%), U238(94%), Pu(0.9%), Fission Products(3.8%), Other Radioactive Isotopes (0.6%) In an open fuel cycle the spent fuel rods will first be subject to storage on site under water (1 year) to bring down the immediate level of radioactivity. Then Intermediate storage (40+ years) under water. At this stage the remaining spent fuel will need long term disposal (1000 years) underground or undersea. In a closed fuel cycle the spent fuel rods are stored on site for about five years and then sent for reprocessing. Reprocessing extracted fissionable material (Uranium and Plutonium) for re-use and remaining high level waste can be sent straight to long term storage. Although reprocessing generates additional fuel the high cost of reprocessing (including transport of extremely hazardous material) means that it is no more cost effective than open fuel cycle. 26

27 Plant De-commissioning The safe decommissioning of nuclear plant at the end of its working life is another externality. Preferred approach in the UK is to remove non active parts of the plant and leave the active parts in situ for approx 135 years (BER) until the levels of radioactivity have declined considerably. Complete demolition can then occur. Proponents of nuclear power estimate decommissioning to be a small element of the overall cost when amortized over the life of the plant. However using the time value of money to calculate the net present value of costs far into the future may be problematic and tends to make future costs seem insignificant. Environmentalists point out that this approach is simply leaving the problem for a future generation to deal with. 27

28 Security Concerns The potential hazard arising from an accident on a nuclear site means that plant may be a target for attack. The transport and storage of enriched fuels and plutonium rich nuclear waste present significant security and safety risks. The concentrations involved in nuclear power generation are significantly lower than those used in nuclear weapons but historically many states have seen the establishment of a nuclear power industry as a stepping stone to nuclear weapons capability. 28

29 Exercise Identify reasons and make a case why Ireland should consider nuclear power generation as a future option. Identify reasons and make as case why Ireland should not consider nuclear power as an option. 29

30 The Future Breeder Reactors could extend available reserves considerably but breeder reactors will inevitably lead to plutonium proliferation and consequent security risks generally not in favour. Concerns over greenhouse gas emissions has brought nuclear power back into focus in many countries Safer Nuclear power station designs pebble bed reactors (fail safe design) Economics New technology (3 rd generation plants ) offer higher efficiencies and in addition fossil fuel prices are rising. Problem of nuclear waste remains to be solved. Public acceptance of nuclear power remains low in many countries. Nuclear Fusion remains the holy grail vast fuel reserves (Deuterium and Tritium from water) and clean reaction products but despite 50 years of intensive research the fusion reactor still seems a long way off. 30

31 Source: Sokolov & McDonald Nuclear Power Global Status and Trends Publication of International Atomic Energy Agency available online from iaea.org 31

32 Source: International Atomic Energy Association Annual Report

33 Questions Why has the IAEA revised upwards it projections for future global nuclear capacity? Is nuclear power green? A famous politician (Tip O Neill) once said that All Politics is local. This is particularly true in Irelands case where multi-seat constituencies mean that elected representatives must not only compete against other parties but also against other members of their own party. Having a strong local presence and being able to deliver on the needs of the local people is considered an absolute must for a candidate to get elected to national office. How do you think this political system might influence Irelands decision whether or not to adopt nuclear power in the future? 33